Engineering crystal structures in nanoscale is challenging, yet provides an effective way to improve catalytic performances. Platinum (Pt)-based nanoframes are a new class of nanomaterials that have great potential as high-performance catalysts. To date, these nanoframes are formed through acid etching in aqueous solutions, which demands long reaction time and often yields ill-defined surface structures. Metallic nanocages are discussed in [38]: synthesis of bimetallic Pt-palladium (Pd) hollow dendritic nanoparticles with dendritic shells by selective chemical etching with nitric acid. Creation of hollow metallic nanostructures is discussed in [39]: one-pot aqueous synthesis of hollow Pd/Pt single-crystalline nanocubes [40] describes hollow Pt spheres with nano-channels: synthesis and enhanced catalysis for oxygen reduction, using silver (Ag) nanoparticles as sacrificial templates. Hollow/rattle-type mesoporous nanostructures by a structural difference-based selective etching strategy, using, for example, ammonia solution as an etchant is discussed in [41]. Pt-centered yolk-shell nanostructure formation by sacrificial nickel (Ni) spacers on a silica core, using a microemulsion methods discussed in [42]. A process for making superparamagnetic CoPt nanospheres is described in [43]. NaBH4 is added to a solution of CoCl2 and poly(vinyl)pyrrolidone, followed by K2PtCl6. A two-step process for preparing porous Pt nanocrystals (NCs) from K2PtCl4 using L-ascorbic acid as the reducing agent is described in [44], following procedures of Meyer et al. [51], without any Na3-citrate added. Synthesis of Pd—Rh core-frame concave nanocubes, and their conversion to Rh cubic nanoframes by selective wet etching of the Pd cores is discussed in [45]. Etched Pt nanoparticles were formed by etching Ag using nitric acid [46], resulting in elementally pure nanocubes.
US 20150236355, expressly incorporated herein by reference in its entirety, provides oleylamine capped PtNi3 polyhedral nanoparticles in hexane and/or chloroform, which are spontaneously converted to Pt3Ni nanoframes, under ambient conditions (laboratory air, having an air pressure within 10% of 101.3 kPa and an overall oxygen content by weight between 18% and 25%), in two weeks. After dispersion of PtNi3 nanoframes onto a high surface area carbon support (e.g., Vulcan XC-72) and subsequent thermal treatment between 370° C. and 400° C., the Pt3Ni nanoframe surfaces tend toward a Pt{111}-skin structure.
The Mond process was originally developed to purify Ni from ore. It treats the ore with carbon monoxide (CO), to complex the Ni separate from other elements. The general process may be applied to form transition metal complexes with Ni, Iron (Fe), Cobalt (Co), Chromium (Cr), Tungsten (W), Molybdenum (Mo), Rhenium (Re), and Ruthenium (Ru), for example. The corresponding formed products are Ni(CO)4, Fe(CO)5, Co2(CO)8, Cr(CO)6, W(CO)6, Mo(CO)6, Re2(CO)10 and RuCO5. It is noted that it is also known that mixed complexes may be formed, only partially carbonylated. It is also known that the transition metals can be pulled off a substrate, or deposited onto a substrate, depending upon temperature and pressure of the carbonyl gas or gas mixture. The various transition metals are shown in Table 3:
The transition elements include Scandium (Sc); Titanium (Ti); Vanadium (V); Chromium (Cr); Manganese (Mg); Iron (Fe); Cobalt (Co); Nickel (Ni); Copper (Cu); Zinc (Zn); Yttrium (Y); Zirconium (Zr); Niobium (Nb); Molybdenum (Mo); Technetium (Tc); Ruthenium (Ru); Rhodium (Rh); Palladium (Pd); Silver (Ag); Cadmium (Cd); Hafnium (Hf); Tantalum (Ta); Tungsten (W); Rhenium (Re); Osmium (Os); Iridium (Ir); Platinum (Pt); Gold (Au); and Mercury (Hg). While highly unstable man-made elements have limited use, Technetium finds the medical application. The lowest oxidation states are exhibited in metal carbonyl complexes such as Cr(CO)6 (oxidation state zero) and [Fe(CO)4]2− (oxidation state −2) in which the 18-electron rule is obeyed. These complexes are also covalent. Ionic compounds are mostly formed with oxidation states +2 and +3. In aqueous solution the ions are hydrated by (usually) six water molecules arranged octahedrally. The reactivity of these transition elements to form carbonylates varies significantly across the range and with different reaction conditions, thus leading to the possibility of differential reactions and separations of the various metals.
The carbonyl or Mond process was discovered in 1884 when Ludwig Mond noticed that hot CO gas would severely corrode Ni. Mond demonstrated that element Ni could be extracted from its ores above 50° C. by CO that acts as both the complex ligand and reducing agent to form a gaseous compound, Ni(CO)4, which is stable up to 230° C. Above 230° C., Ni and CO can be recovered again from the decomposition of Ni(CO)4. The process exploits the ability of CO to form compounds with transition elements from the vanadium group to the nickel group of the periodic table. These transition elements undergo carbonyl or carbonyl+additional gas reactions. The process works particularly well for Ni, Fe, and Co and is most mature in these alloy systems. A known process for winning Ni operates by treating an aqueous ammonium salt solution of Ni salts with a CO-containing gas under reducing conditions to produce nickel carbonyl and subsequently recovering Ni. Optionally, the production of nickel carbonyl can be catalyzed, for example, by cyanide. Also, an essentially water-immiscible solvent for nickel carbonyl can optionally be employed. The aqueous ammoniacal solution is typically an aqueous ammoniacal ammonium chloride, carbonate, sulfate, hydroxide, or mixture thereof. The valuable metals associated with Ni, e.g., Cu, Co, Fe, and precious metals, are also separated and recovered by this process.
See, U.S. Pat. Nos. 9,309,121; 9,023,402; 8,852,315; 8,840,552; 8,759,058; 8,722,270; 8,703,089; 8,404,226; 8,287,838; 8,124,347; 7,967,891; 7,964,220; 7,910,680; 7,892,687; 7,799,315; 7,790,189; 7,776,129; 7,767,643; 7,625,410; 7,606,274; 7,410,941; 7,345,019; 7,309,687; 7,270,728; 7,198,770; 7,011,854; 6,924,049; 6,828,054; 6,770,394; 6,751,516; 6,746,511; 6,649,299; 6,641,767; 6,506,229; 6,007,634; 5,736,109; 5,541,003; 5,532,292; 5,362,580; 5,197,993; 5,147,687; 5,146,481; 5,092,967; 5,052,272; 5,010,804; 4,734,219; 4,659,426; 4,579,722; 4,315,757; 4,273,724; 4,243,644; 4,160,745; 4,137,259; 3,967,958; 0,455,230; 20160258053; 20160189816; 20130126295; 20120220010; 20120204680; 20110277590; 20110237546; 20110111310; 20110059009; 20110017493; 20100275731; 20100273149; 20100246610; 20090297709; 20080267810; 20070277648; 20070061006; 20070034053; 20070007121; 20060276493; 20060233890; 20060148900; 20050233187; 20050044991; 20050013771; 20040241063; 20040204785; 20040109810; 20040067261; 20040003680; 20030157347; 20020102446; 20020088306; 20010033956; 20010031389; and 20010026884, each of which is expressly incorporated herein by reference in its entirety.